use local variables to hold unique classes

Author: sycai

bigframes/ml/metrics/_metrics.py

@@ -331,18 +331,15 @@ def _precision_score_per_class(y_true: bpd.Series, y_pred: bpd.Series) -> pd.Ser
 def _precision_score_binary_pos_only(
     y_true: bpd.Series, y_pred: bpd.Series, pos_label: int | float | bool | str
 ) -> float:
-    if (
-        y_true.unique(keep_order=False).count() != 2
-        or y_pred.unique(keep_order=False).count() != 2
-    ):
+    y_true_classes = y_true.unique(keep_order=False)
+    y_pred_classes = y_pred.unique(keep_order=False)
+
+    if y_true_classes.count() != 2 or y_pred_classes.count() != 2:
         raise ValueError(
             "Target is multiclass but average='binary'. Please choose another average setting."
         )
 
-    total_labels = set(
-        y_true.unique(keep_order=False).to_list()
-        + y_pred.unique(keep_order=False).to_list()
-    )
+    total_labels = set(y_true_classes.to_list() + y_pred_classes.to_list())
 
     if len(total_labels) != 2:
         raise ValueError(